From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from galois.linutronix.de (Galois.linutronix.de [193.142.43.55]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id BA0F53ECBD2; Tue, 20 Jan 2026 08:01:07 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=193.142.43.55 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1768896069; cv=none; b=UtJURdTl+k9KecFYRNUFE7AZKxHnhpQ+qu+mh6L7qOzSb5SS1QoLw/JJkV2K5ROFRbCJYQW6OFjlKoSaT66oVHn7f9pYoWL67xVGMZwR8+dGNopw6jTQEprbpxm8GuK40kJ3Rxua33h8GCV6PtorbhCIYdekUvYTtLobIxjgsGY= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1768896069; c=relaxed/simple; bh=RmSONWxhlOTRon66C5OvbQm5Uu4yj8N6syflI7E2r94=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=rlk0U4E3sawhp9F0o4l0eKvTM6NBuK+2UFXo+r8mQODzd+ax7ed4WnkxFCMqwAB/Kc/LuSyTb+4CndeKWhYn/kPUkx7NTuuoDyMn5Jx+fUWcHuJfmJvbv732nqYF6m03wYvgaNayymO1GeGJbWg4kiEJ3ljIAwYYzQNzawsknNU= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linutronix.de; spf=pass smtp.mailfrom=linutronix.de; dkim=pass (2048-bit key) header.d=linutronix.de header.i=@linutronix.de header.b=aD0nDc9f; dkim=permerror (0-bit key) header.d=linutronix.de header.i=@linutronix.de header.b=Fha83y4m; arc=none smtp.client-ip=193.142.43.55 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linutronix.de Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linutronix.de Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=linutronix.de header.i=@linutronix.de header.b="aD0nDc9f"; dkim=permerror (0-bit key) header.d=linutronix.de header.i=@linutronix.de header.b="Fha83y4m" Date: Tue, 20 Jan 2026 09:01:04 +0100 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1768896066; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=Hpegz2UFo69eXg0vefVrJoKsoZDXsC5W1aFCrRzd8CU=; b=aD0nDc9fmotbeEvKlmW+0NRHteRu0DtQPjp+DQu68qFcNpiAEZ1Olc9VJROQi1LRIGZPjb QPBvoCEaxVnhbG0D+3EFDZYvCZDGY/vgswYkYBVS/lpaAW6zy/te/6Y/ufvNMpazVmLy52 WtKCc2VoAIwTo5UwilM0mfoQtLZ+rhsCmfSgFfKEtPQUnbGjBpA4tPOMIk55Epeuq+sjP8 Q0M/OrANUr5vsfVKtEOnAOtns0A0IV1dHWztYV1Eo6uieI+vLGIuFO+lrhMqBls7amUWN6 ZAre1mqzOAKRkzVrin/HfpYMIFvXyOqKujSjlZQ5+FrJTOQEx9rWKOqH/AD+1Q== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1768896066; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=Hpegz2UFo69eXg0vefVrJoKsoZDXsC5W1aFCrRzd8CU=; b=Fha83y4mAFlYmogNkePwXJD5ZnJs+t45w0hkB1V7eKbrTyo6ZAsQhYiREU/NX8L8OzpdAj HloYO6HuwUT7ypCA== From: Sebastian Andrzej Siewior To: Greg Kroah-Hartman Cc: Jakub Kicinski , wen.yang@linux.dev, stable@vger.kernel.org, linux-kernel@vger.kernel.org, Paolo Abeni Subject: Re: [PATCH 6.6 3/3] net: Allow to use SMP threads for backlog NAPI. Message-ID: <20260120080104.0yYtfQR7@linutronix.de> References: <997bc0de4746100bb69e1bd2ccfb25315d8f62e4.1768751557.git.wen.yang@linux.dev> <20260119082534.1f705011@kernel.org> <20260119163026.aA1PeSmP@linutronix.de> <2026012040-unmolded-dreaded-6e06@gregkh> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <2026012040-unmolded-dreaded-6e06@gregkh> On 2026-01-20 07:03:58 [+0100], Greg Kroah-Hartman wrote: > On Mon, Jan 19, 2026 at 05:30:26PM +0100, Sebastian Andrzej Siewior wrote: > > On 2026-01-19 08:25:34 [-0800], Jakub Kicinski wrote: > > > On Mon, 19 Jan 2026 00:15:46 +0800 wen.yang@linux.dev wrote: > > > > From: Sebastian Andrzej Siewior > > > > > > > > commit dad6b97702639fba27a2bd3e986982ad6f0db3a7 upstream. > > > > > > > > Backlog NAPI is a per-CPU NAPI struct only (with no device behind it) > > > > used by drivers which don't do NAPI them self, RPS and parts of the > > > > stack which need to avoid recursive deadlocks while processing a packet. > > > > > > This is a rather large change to backport into LTS. > > > > I agree. While I saw these patches flying by, I don't remember a mail > > where it was justified why it was needed. Did I miss it? > > Please see patch 0/3 in this series: > https://lore.kernel.org/all/cover.1768751557.git.wen.yang@linux.dev/ The reasoning why this is needed is due to PREEMPT_RT. This targets v6.6 and PREEMPT_RT is officially supported upstream since v6.12. For v6.6 you still need the out-of-tree patch. This means not only select the Kconfig symbol but also a bit futex, ptrace or printk. This queue does not include the three patches here but has another workaround having more or less the same effect. If this is needed only for PREEMPT_RT's sake I would suggest to route it via the stable-rt instead and replace what is currently there. Sebastian